The present invention relates to a DA converter for converting an input digital value into an analog signal.
There is known in the art such a DA converter in which a plurality of resistors are connected in series, a fixed voltage is applied across the series connection, the connection points of the resistors are respectively connected via switches to an output terminal and one of the switches is turned ON in accordance with an input digital value, whereby to obtain an analog voltage at the output terminal. In another conventional DA converter, a power source is connected to one end of a ladder network composed of series resistors of a resistance value R and shunt resistors of a resistance value 2R in each section and, by effecting such a control that the shunt resistors of the respective sections of the ladder network are connected to an output amplifier or a common potential point corresponding to respective bits of the input digital value, an analog output is obtained.
In such prior art DA converters, it is necessary to enhance the accuracy of the resistance value of each resistor according to the required conversion accuracy. To obtain a resistor of high resistance value, it is customary in the prior art to employ a winding resistor formed by a resistance wire of extremely small temperature coefficient and to adjust each resistance value with high accuracy. This adjustment is troublesome, and hence makes the DA converter expensive and, in addition, the use of such a winding resistor makes the DA converter bulky.